The present invention relates to electro-optic, semi-conductor probes for measurement of electric and thermal fields.
The electrothermal behavior of active microwave and millimeter-wave circuits has received growing attention in recent years. The thermal characteristics become especially important in active antenna arrays and quasi-optical power-combining structures where a multitude of biased monolithic microwave integrated circuits (MMICs) are in close proximity. The generation of heat in such configurations mandates a strong consideration of heat dissipation in the overall design.
Several methods have been developed to characterize and diagnose the behavior of such circuits. To examine the electrical behavior, optical techniques such as those that use electrooptic probes for the noncontact field mapping of electric fields have been employed. Separate methods exist for observing thermal effects including the use of thermal cameras, IR microscopes, thermocouples, and thermistors.
A major factor that has until now, not been considered when applying electrooptic field-mapping techniques to the characterization of active microwave circuits is the temperature dependence of the probe itself. The electrooptic coefficients that govern the response of the probe to RF fields are known to vary with temperature. Additionally, in III-V semiconductor-based probes, the temperature dependence of the optical absorption edge is significant. The sensitivity of the absorption edge to temperature has been used, for example, to monitor the temperature in indium-phosphide-based semiconductor substrates where knowledge of the epitaxial growth temperature is critical.
Thus, it would be desirable to provide an integrated electro-thermal probe which is capable of addressing the temperature-dependant effects associated with gallium-arsenide electrooptic probes. It would also be desirable to provide an integrated electro-thermal probe which is capable of simultaneously measuring both electric and thermal fields to allow for the combined electrothermal examination of active microwave and millimeter-wave circuits with a single probe and the ability to calibrate electric field data that is corrupted when the probe is placed in areas where temperature variations are present.